The present invention relates to digital signal processing, and more particularly to video devices and processing methods.
Image stabilization (IS) refers to the task of eliminating jitter from video sequences captured by handheld cameras. Jitter is typically due to the undesired shake of the camera user's hand during video recording, and becomes a more severe problem when high zoom ratios are used. Eliminating jitter from video sequences has been an increasingly important problem for consumer digital cameras and camera phones. There are a few different approaches to the solution of the image stabilization problem. One particular approach is to use digital image processing techniques to eliminate jitter. This approach is generally called digital image stabilization (DIS).
A typical digital image stabilization method can be summarized as follows:
Step 1: Motion vector computation: Compute a number of candidate motion vectors between two frames by finding the correlations between blocks of pixels.
Step 2: Global motion vector determination: Process these candidate motion vectors using a number of heuristics to find the global motion between the two frames that is due to jitter.
Step 3: Motion compensation: Compensate for the estimated jitter motion by digitally shifting the output image in the reverse direction of the motion.
For example, U.S. Pat. No. 5,563,652 divides a image into four detection areas; within each detection area compares pixels of the current image with representative pixels of the prior image to find the best offset correlation; analyzes the best correlation to the average plus analyzes gradients to check whether the detection area is a valid detection area for jitter detection; and for invalid areas uses prior image(s) average motion vector(s) to compute a whole image motion vector. U.S. Pat. No. 5,748,231 matches binary edge patterns in motion estimation areas of successive fields to find local motion vectors; combines the local motion vectors with weights from correlation statistics to find field motion vectors; and accumulates the field motion vectors. U.S. Pat. No. 6,628,711 compares motion vector histograms for successive images to estimate jitter.